The nature of ordered structures in melt spun iron-silicon alloys

Abstract

Increasing the silicon content is known to improve the magnetic properties of iron-silicon alloys (I). However, the associated loss of ductility has prevented the use of high silicon alloys in practical applications. The melt spinning of high silicon alloys can,produce wide tapes with reasonable ductility that are now regarded as one of the promising materials for magnetic applications (2-8). Investigations of the magnetic and mechanical properties consistently indicate a variation with silicon content (2- , 8-II). The best property combinations seem to exist for 6.5 wt % silicon alloy. Narita and Enokizono (10) have shown that in bulk Fe-Si alloys with high silicon contents, the B2 and DO₃ ordering lead to different property changes and that cooling rate has major influence on magnetic properties. The magnetic and mechanical properties of rapidly solidified melt spun alloys are shown to be significantly different (3-5,7- 10-12). For example, the permeability of melt spun tapes is different for different alloys. It has a maximum value for a 6.5 wt % Si alloy which is different behavior from that observed in a well annealed sample (12). In order to understand the reasons for such behavior, a clear understanding of the structure is necessary. There exists considerable confusion in the literature regarding the structure of the melt spun alloys (3-5,7-8,13). For example, DO₃ ordering is assumed to be predominant in melt spun 6.5 wt %'SJ alloy by many investigators (4-7). Chang et al. (5) have presented TEM evidence of it Jn the shape of a 010 superlattice spot observable Jn a [100] zone selected area diffraction pattern. However, this is not adequate to differentiate between the B2 and DO₃ ordering. A different conclusion that the structure is a predominantly disordered phase (A2) with a very small amount of B2, was reported by Enokizono et al. (3). They have also reported the absence of domain structure. Guntherodt (7) and Warlimont (8) highlighted the suppression of the ordering reaction by melt spinning as the main reason for the improved ductility of the melt spun tapes.